This invention relates to a device for use in Molten Carbonate Fuel cell stacks in an effort to equalize electrolyte content throughout the stack during operation.
Molten Carbonate Fuel Cells are well known and described in many prior publication and patents, e.g. U.S. Pat. No. 4,407,267 to Iacovangelo et al. Typically porous, sintered Ni-Cr anodes and porous NiO cathodes are disposed on opposite major surfaces of a porous electrolyte tile. A tile of such as lithium aluminate (LiAlO.sub.2), or other inert ceramic is filled with molten alkali metal carbonate electrolyte, (e.g. Li.sub.2 CO.sub.3 /K.sub.2 CO.sub.3) in each cell in a fuel cell stack. Stacks with several hundred fuel cells are contemplated in a typical power supply. Severe electrolyte redistribution has been observed even in experimental stacks with substantially fewer cells than that expected for an operational power supply.
The exact mechanism by which the electrolyte migrates is not clearly understood. Nonetheless, it is known that the cells near the negative end of the stack become flooded while the cells towards the positive end of the stack become depleted or dry of molten electrolyte. Some have suggested that an electrical shunt current through the manifold gasket causes electrolyte migration toward the negative end of the stack. The depletion of electrolyte severely impairs the performance of the affected cells and greatly increases the overall resistence of the stack.
The efforts to limit electrolyte redistribution have not been completely successful. Ordinarily, the fuel cell stack is arranged with the positive end at the bottom and the negative end at the top so that gravity will resist migration of electrolyte toward the more negative cells. However, this has not proven sufficient to prevent redistribution of electrolyte towards the upper cells. Others have modified electrode and stack component properties with some sucess to limit electrolyte migration. However, such modifications have unneccessarily added to the complexity and cost of the cell stack.
Therefore, in view of the above, it is an object of the present invention to provide a device for equalizing the electrolyte content along the height of a fuel cell stack.
It is a further object to provide means for returning electrolyte from the negative to the positive end of a fuel cell stack during operation.
It is also an object to provide a device to effect equalization of electrolyte content throughout a fuel cell, stack height without unnecessarily adding to the stack complexity.